As computer processing has moved from local compute resources, such as a desktop or laptop computer system, to remote distributed compute resources, such as cloud-host services and the like, data transfer speeds across networks has become increasingly important. To this end, high-speed network links are critical for data center and high performance computing (HPC). One of the primary network technologies in data centers and HPC environments is high-speed Ethernet.
The original Ethernet standard was specified in Institute of Electrical and Electronics Engineers (IEEE) 802.3 in 1983. Subsequently, the vast majority of Ethernet standards have been developed and specified under an IEEE 802.3-based committee. The IEEE 802.3 Ethernet standard defines several data rates that can be used when connecting two systems. For the backplane and copper cables media, there is an auto-negotiation (AN) protocol defined in clause 73 of the standard (803.2-2012, Section Five), which enables selecting a port type, and other features such as forward error correction (FEC), based on advertised capabilities of both sides. Network management can be used to program what capabilities are advertised for a port, and thus control the data rate that will be selected by AN. For some rates, a link training period is included in the AN process, which enables improving received signal quality and operating over more challenging media (e.g. longer cables).
In contrast, the implementation of Ethernet operation over copper cables at 10 Gigabit per second (Gb/s) was defined outside of IEEE 802.3, in the Small Form Factor (SFF)-8418 committee, and labeled (Small Form Factor Pluggable) SFP+ direct attach or 10GSFP+Cu, also known as 10G Direct Attach Cable or 10G DAC. The form factor and electrical interface for 10G DAC are specified by a multi-source agreement, is widely-used in today's data centers and is envisioned to continue to see substantially usage in the future. In contrast to the 802.3 standard, 10G DAC does not support either auto-negotiation or FEC, nor is link training supported.